1. Field of the Invention
This invention is directed to methods for extracting leachable materials from a hydratable polymer such as a xerogel material. In one embodiment, the extraction is conducted after hydration of the hydratable polymer. In another embodiment, extraction is conducted simultaneously with hydration of this polymer to a hydrogel material. In either case, the resulting hydrogel material can then be used in ophthalmic devices such as intraocular lenses, contact lenses, etc.
In the methods of this invention, extraction procedures are simplified by incorporation of an adsorbent into the solution which facilitates extraction of the leachable materials from the hydratable polymer. When the extraction solution is water and the hydratable polymer is in its xerogel form, hydration of the hydratable polymer to the hydrogel material occurs simultaneously with extraction.
This invention is further directed to a sealed package for shipping/storing hydrogel materials in the form of ophthalmic devices which incorporates water and an adsorbent into the package which adsorbent effects selective retention of leachable components from the ophthalmic device. These packages are particularly useful for in situ conversion of a xerogel material to a hydrogel material in the form of an ophthalmic device with concomitant extraction of the leachable components from the device. When so employed, the xerogel form of the ophthalmic device can be directly packaged and shipped for consumer use while permitting hydration and extraction to occur in situ thereby providing for a hydrated ophthalmic device suitable for consumer use.
2. State of the Art
The preparation of hydrogel ophthalmic devices, e.g., soft contact lenses, for consumer use is a multi-step process. In addition to the important concerns relating to manufacturing a contact lens or other ophthalmic device which is appropriately fitted for the particular consumer's needs, the ophthalmic device manufacturing process must include process steps for removal of leachable materials from the hydratable polymer used in the device.
Specifically, soft hydrogel ophthalmic devices are prepared by polymerizing a monomeric composition to a dry hydratable polymer typically referred to in the an as a "xerogel" or a "xerogel material". The as-prepared xerogel material typically contains leachable materials such as unreacted monomers and partially reacted oligomers. Contamination of the xerogel material with such monomers and oligomers is undesirable since these materials are toxic and, during use, can leach into the eye fluid causing, for example, eye irritation and other problems. Accordingly, the U.S. Food and Drug Administration (FDA) has set standards relative to maximum monomer/oligomer concentration in ophthalmic devices for consumer use. In order to meet these standards, a portion of the leachable materials must be removed from the polymer composition which removal is typically achieved by several washings of the ophthalmic devices using water, ethanol, or other suitable solvents. When using such solvents, a portion of the leachable materials, including the unreacted monomers and partially reacted oligomers, are transferred under a mass-transfer mechanism to the solvent which solvent is subsequently discarded. This washing step is repeated until leachable contamination in the ophthalmic device is reduced to acceptable levels.
When water is used as the washing material, the washing steps also result in hydration of the hydratable polymer from its xerogel to its hydrogel form. When ethanol or other non-aqueous solvents are employed in the washing steps, then a separate hydration step is afterwards required to form the final hydrogel.
After extraction/hydration, the ophthalmic device is typically inserted into a sealed package containing an aqueous buffered solution for shipment and storage prior to consumer use. The inclusion of the aqueous buffered solution in the package is necessary to insure against dehydration of the hydrated ophthalmic device.
In any event, the process of effecting formation of a hydrated ophthalmic device from a hydratable polymer in the form of a xerogel material involves numerous extraction/hydration steps which necessarily hinder efficient manufacture of ophthalmic devices prior to packaging of these devices into end use form. Additionally, the presence of leachable materials in the discarded solvent can cause disposal problems.
In addressing this problem, the art has described methods which result in the extraction of leachable materials to a desired level. For example, Kindt-Larsen, U.S. Pat. No. 5,080,839, discloses a process wherein the contact lens is placed into a cavity defined by a first and a second carrier element which both confines and maintains a proper orientation for the lens. A fluid flow is then introduced through the cavity to effect flushing of the leachables from the lens which fluid flow can be repeated as necessary to effect reduction of the leachables to a desired level. Allegedly, the use of such a fluid flow through this cavity results in more efficient removal of the leachables from the lens and reduces the need to physical manipulate the lens while maintaining a proper orientation of the lens in the cavity.
However, notwithstanding the advantages of this method, there is a continuing need in the art to simplify the extraction/hydration steps required to form an ophthalmic device having acceptable contaminant (i.e., leachable material) concentration. In this regard, it would be particularly advantageous if the extraction/hydration step could be coupled with a packaging step so as to provide for an overall efficient method for preparing and packaging an ophthalmic device for consumer use.